Water incorporation in synthetic and natural MgAl₂O₄ spinel     

Geoffrey D. Bromiley  Fabrizio Nestola  Ming Zhang 《Geochimica et cosmochimica acta》2010,74(2):705-445

The solubility and incorporation mechanisms of water in synthetic and natural MgAl₂O₄ spinel have been investigated in a series of high-pressure/temperature annealing experiments. In contrast to most other nominally anhydrous minerals, natural spinel appears to be completely anhydrous. On the other hand, non-stoichiometric Al-rich synthetic (defect) spinel can accommodate several hundred ppm water in the form of structurally-incorporated hydrogen. Infrared (IR) spectra of hydrated defect spinel contain one main O-H stretching band at 3343-3352 cm⁻¹ and a doublet consisting of two distinct O-H bands at 3505-3517 cm⁻¹ and 3557-3566 cm⁻¹. IR spectra and structural refinements based on single-crystal X-ray data are consistent with hydrogen incorporation in defect spinel onto both octahedral and tetrahedral O-O edges. Fine structure of O-H bands in IR spectra can be explained by partial coupling of interstitial hydrogen with cation vacancies, or by the effects of Mg-Al disorder on the tetrahedral site. The concentration of cation vacancies in defect spinel is a major control on hydrogen affinity. The commercial availability of large single crystals of defect spinel coupled with high water solubility and similarities in water incorporation mechanisms between hydrous defect spinel and hydrous ringwoodite (Mg₂SiO₄) suggests that synthetic defect spinel may be a useful low-pressure analogue material for investigating the causes and consequences of water incorporation in the lower part of Earth’s mantle transition zone.  相似文献   

Antigorite equation of state and anomalous softening at 6 GPa: an in situ single-crystal X-ray diffraction study   总被引：1，自引：0，他引：1  

Fabrizio Nestola  Ross J. Angel  Jing Zhao  Carlos J. Garrido  Vicente López Sánchez-Vizcaíno  Giancarlo Capitani  Marcello Mellini 《Contributions to Mineralogy and Petrology》2010,160(1):33-43

The compressibility of antigorite has been determined up to 8.826(8) GPa, for the first time by single crystal X-ray diffraction in a diamond anvil cell, on a specimen from Cerro del Almirez. Fifteen pressure–volume data, up to 5.910(6) GPa, have been fit by a third-order Birch–Murnaghan equation of state, yielding V ₀ = 2,914.07(23) Å³, K _T0 = 62.9(4) GPa, with K′ = 6.1(2). The compression of antigorite is very anisotropic with axial compressibilities in the ratio 1.11:1.00:3.22 along a, b and c, respectively. The new equation of state leads to an estimation of the upper stability limit of antigorite that is intermediate with respect to existing values, and in better agreement with experiments. At pressures in excess of 6 GPa antigorite displays a significant volume softening that may be relevant for very cold subducting slabs.  相似文献   

Effects of interplanetary dust on the LISA drag-free constellation     

Massimo Cerdonio  Fabrizio De Marchi  Roberto De Pietri  Philippe Jetzer  Francesco Marzari  Giulio Mazzolo  Antonello Ortolan  Mauro Sereno 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):255-264

The analysis of non-radiative sources of static or time-dependent gravitational fields in the Solar System is crucial to accurately estimate the free-fall orbits of the LISA space mission. In particular, we take into account the gravitational effects of Interplanetary Dust (ID) on the spacecraft trajectories. The perturbing gravitational field has been calculated for some ID density distributions that fit the observed zodiacal light. Then we integrated the Gauss planetary equations to get the deviations from the LISA Keplerian orbits around the Sun. This analysis can be eventually extended to Local Dark Matter (LDM), as gravitational fields are expected to be similar for ID and LDM distributions. Under some strong assumptions on the displacement noise at very low frequency, the Doppler data collected during the whole LISA mission could provide upper limits on ID and LDM densities.  相似文献   

Integrated stratigraphy (cyclostratigraphy and biochronology) of late Middle Miocene deposits in the Mediterranean area and comparison with the North and Equatorial Atlantic Oceans: synthesis of the major results     

Fabrizio Lirer  Silvia Iaccarino 《地学学报》2005,17(4):338-349

The stratigraphic correlation of North and Equatorial Atlantic Ocean records with Mediterranean astronomically tuned sections reveals the diachrony of several planktonic foraminiferal bioevents, but shows the possibility to adopt the Mediterranean biostratigraphy in North Atlantic records. These data provide new tools for biostratigraphic correlation, mainly between the Mediterranean and the North Atlantic areas. Quantitative analyses carried out on planktonic foraminifera reveal the occurrence at Site 982-HoleB (ODP Leg 162) of some bioevents in the same order as those recorded in Mediterranean sequences. In addition, Neogloboquadrina atlantica praeatlantica first occurrence (FO) [within the short range of Paragloborotalia mayeri, sensuRiv. Ital. Paleontol. Stratigr. 108 (2002) 257] occurs in levels older than its FO in the Mediterranean area where it first appears at the same level as N. acostaensis s.s. coinciding with the last occurrence of P. partimlabiata. In agreement with the findings of Poore [Init. Rep. Deep Sea Drilling Proj. 49 (1979) 447] and the hypothesis of Zachariasse and Aubry [Paleobios 16 (1994) 68], the first representative of the neogloboquadrinids originated north of Iceland and migrated towards the southern latitudes at different times, first in the Mediterranean and mid-latitude Atlantic Ocean, then in low-latitudes (Site 397).  相似文献   

Coastal deformation between the Versilia and the Garigliano plains (Italy) since the last interglacial stage     

Marco F. Nisi  Fabrizio Antonioli  Giuseppe Dai Pra  Gabriele Leoni  Sergio Silenzi 《第四纪科学杂志》2003,18(8):709-721

The opening of the north‐central Tyrrhenian Sea is the result of the Cretaceous–Paleogene alpine collision, which triggered a series of regional uplift, subsidence and transcurrent tectonic mechanisms along the coastal Tyrrhenian sectors of peninsular Italy. These tectonic processes, in conjunction with the effects of glacio‐ and hydro‐isostasy during the Quaternary, produced substantial crustal responses that, in some cases, reached metres in extent. In the study of coastal neotectonics, geomorphological markers of the last interglacial maximum, corresponding to marine isotope stage 5.5, are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr. Through altimetrical, palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913, combined with an additional set of data reported here, a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern Tuscany and southern Latium is presented. The reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors. This has been done by carefully choosing the eustatic marker, among those available at each study site, in order to minimize the margin of error associated with the measurements. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

The morphology–density relation in the Sloan Digital Sky Survey     

Tomotsugu Goto †  Chisato Yamauchi  Yutaka Fujita  Sadanori Okamura  Maki Sekiguchi  Ian Smail  Mariangela Bernardi  Percy L. Gomez 《Monthly notices of the Royal Astronomical Society》2003,346(2):601-614

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Active normal faulting along the Mt. Morrone south-western slopes (central Apennines,Italy)     

Stefano Gori  Biagio Giaccio  Fabrizio Galadini  Emanuela Falcucci  Paolo Messina  Andrea Sposato  Francesco Dramis 《International Journal of Earth Sciences》2011,100(1):157-171

In the present work we analyse one of the active normal faults affecting the central Apennines, i.e. the Mt. Morrone normal fault system. This tectonic structure, which comprises two parallel, NW-SE trending fault segments, is considered as potentially responsible for earthquakes of magnitude ≥ 6.5 and its last activation probably occurred during the second century AD. Structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure, fitting an approximately N 20° trending extensional deformation. Geological and geomorphological investigations performed along the whole Mt. Morrone south-western slopes permitted us to identify the displacement of alluvial fans, attributed to Middle and Late Pleistocene by means of tephro-stratigraphic analyses and geomorphological correlations with dated lacustrine sequences, along the western fault branch. This allowed to evaluate in 0.4 ± 0.07 mm/year the slip rate of this segment. On the other hand, the lack of synchronous landforms and/or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch. Nevertheless, basing on a critical review of the available literature dealing with normal fault systems evolution, we hypothesised a total slip rate of the fault system in the range of 0.4 ± 0.07 to 0.8 ± 0.09 mm/year. Moreover, basing on the length at surface of the Mt. Morrone fault system (i.e. 22–23 km) we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6.6–6.7.  相似文献   

Loggerhead turtles Caretta caretta (Linnaeus) preying on the invading gastropod Rapana venosa (Valenciennes) in the Río de la Plata Estuary     

Alvar Carranza  Andrés Estrades  Fabrizio Scarabino  Angel Segura 《Marine Ecology》2011,32(2):142-147

Here we report the first observations of loggerhead turtles Caretta caretta preying on a conspicuous molluscan invader, the rapa whelk Rapana venosa. An average number of 136 opercula were found in stomach contents of five turtles, the curved carapace length ranging in from 51 to 112 cm. No other alimentary items were found in the turtles analyzed. We suggest that the rapa whelk may constitute up to 100% of the diet for immature and mature loggerheads in the Río de la Plata estuary (Uruguay), highlighting the plastic nature of the foraging behavior of loggerheads.  相似文献   

The effect of sewage discharge on the ecosystem engineering activities of two East African fiddler crab species: consequences for mangrove ecosystem functioning   总被引：1，自引：0，他引：1  

Bartolini F  Cimò F  Fusi M  Dahdouh-Guebas F  Lopes GP  Cannicci S 《Marine environmental research》2011,71(1):53-61

A number of studies have suggested that mangrove forests and their faunal components may be pre-adapted to the impact of organic waste discharge, making them possible natural wastewater treatment wetlands. However, the results from recent research are contradictory. Some studies have shown that negative effects, sometimes subtle and difficult to observe, can be detected on specific biotic components of forests subjected to organic pollution. Therefore, the aim of the present study was to investigate possible alterations in the ecosystem engineering activities of a fiddler crab community dominating the landward belts of Kenyan mangrove forests. The total processed sediment produced by burrowing and foraging activities in a population from a peri-urban mangrove area receiving untreated domestic sewage was compared with that from a forest not affected by urban wastewater. The results showed how the peri-urban site hosted a higher biomass of crabs, which produced a significantly lower amount of processed sediment compared with the pristine site, resulting in a lower total top sediment mixing activity of the crabs. Thus, the present study showed a link between sewage exposure and top sediment reworking by crabs, which is potentially beneficial for mangrove growth and ecosystem functioning. This represents a possible example of cryptic ecological degradation in mangal systems.  相似文献   

1.4-GHz polarimetric observations of the two fields imaged by the DASI experiment     

G. Bernardi  E. Carretti †  R. J. Sault  S. Cortiglioni  S. Poppi 《Monthly notices of the Royal Astronomical Society》2006,370(4):2064-2070

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